In practice, extrusion heads of this type are already widely used in conjunction with one or more extruders. The head parts are adapted to be moved into a rest position for the purposes of cleaning or retrofitting.
Extrusion heads for the processing of rubber mixtures require, in addition to the closed operative position, also an opened rest position in which flow ducts of the extrusion head can be exchanged or cleaned. In the operative position, the head parts have to withstand the pressure of the rubber mixture. The driving power required for pivoting the head parts into the rest position, on the one hand, and for fixing them in the closed operative position, on the other hand, is applied in this case by a plurality of drive means, in particular hydraulic cylinders.
Extrusion heads known as clamp heads, in which two lateral clamps disposed opposite one another fix the two head parts in the operative position, respectively, are already known in practice. Clamps of this type are able to absorb much greater forces than the hydraulic piston/cylinder units used to move the clamps. For this purpose, the clamps have a respective contact face forming a clamping plane, so displacement toward the side of the extrusion head facing the extruders increases the clamping forces, as disclosed by DE 22 01 631 C3 and DE-OS 22 36 363, in which the holding-together forces are absorbed by clamps which are displaced by piston/cylinder units and secured in their closed position.
It is known from that DE-OS 22 36 363 to join together the movable part and the pivotable part of a wide extrusion head, using pivotable clamps which are pressed into their clamp seat by hydraulic piston/cylinder units.
It has been found to be a disadvantage in this regard that, in order to adjust the rest position, the clamp first has to be detached by the drive means and subsequently be pivoted out of the opening region of the head parts by a further drive means.
Also already known are extrusion heads known as hammer heads, in which each of the head parts has associated therewith two respective external, substantially parallel tension elements, of which a tension element head engages a corresponding recess in the respective head part in the operative position, thereby allowing the required pressure force to be applied by the tension elements.
DE 42 36 120 C1 has already described an extrusion head of this type for an extrusion system in the rubber or plastics processing industry, comprising a stationary head part which is to be flanged onto the extrusion system and at least one head part which rests against the extrusion strip, can be pivoted for cleaning purposes and is hingedly attached to the stationary head part by a joint. In the operative position, the head parts are for this purpose clamped to the stationary part by a pair of tie actuated by a respective piston/cylinder unit, and can be pivoted into the rest position by a further piston/cylinder unit.
DE 34 30 062 C2 and, in another embodiment, DE 37 36 231 A1 also disclose a respective extrusion head in which the movable parts of the extrusion head apply the high closing forces required, merely by means of piston/cylinder units. This necessitates the use of very powerful piston/cylinder units.
In the case of DE 34 30 062 C2, one end of the piston/cylinder unit is hingedly attached to the stationary part of the extrusion head in an outwardly pivotable manner. During the opening process, the piston/cylinder unit is pressed outward under the influence of this link, so the tie rods are pivoted out of the path of movement of the pivotable extrusion head parts to allow the opening thereof.
In addition, DE-OS 24 57 532 discloses a single extrusion head with two movable head halves, the common parting plane of which passes through the axis of the extruder, each two movable head halves forming a further parting plane or pair of pressure faces against the end face of the extruder. In this known extruder, a respective hydraulic cylinder is hingedly attached to the cylinder of the screw-type extruder centrally at the top and bottom, the piston rod of each hydraulic cylinder on a double lever having the function of releasing and fixing the cartridge and the profile strip and of opening, closing and fixing the head parts. Apart from the fact that this closing system is limited to an extrusion head with two movable head parts, clamps have to be pivoted to the side to open and close the head parts of this extrusion head also.
In any case, the tension frames have to be pivoted out to the side when the movable head parts are to be raised or lowered to open the feed ducts. However, the pivoting-out of the tension frames, which are already very wide, to the side, requires a large amount of space. In addition, the hydraulic cylinders, which are likewise pivotable for this purpose, have to be connected to a pressure source via flexible lines.
Also known is a construction in which the head parts are pivotably movable in the conventional manner about joints disposed on either side of a longitudinal axis, by means of a single drive means associated with the respective head part. The drive means, which are constructed as hydraulic cylinders, have the function in this case of transmitting the holding force and the sealing forces in the operative position and also of pivoting into the rest position and are for this purpose disposed substantially at right angles to the longitudinal axis. The resulting much greater dimensions have been found to be a disadvantage in this regard.
DE 39 23 290 C1 relates to an extruder head for producing profiles which are made of diverse mixtures of rubbers and/or plastics materials and are extruded from a plurality of extruders, with at least one movable head part. In this case a drive means has the function of generating the closing force for pressing the main parts together and also acts as a wedge-shaped locking device having clamps.